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After completing a study this summer of potential new water supplies for the greater Novato area, the North Marin Water District is exploring two options to bolster storage and drinking water production at its Stafford Lake reservoir.

The yearlong study began in July 2021 after the district and the 61,000 Novato-area residents it serves were feeling the strain of two years of severely dry conditions. The 2020-2021 rainy season was the district’s driest on record, with only 8 inches of rain falling at Stafford Lake, its only local reservoir. The lake normally sees about 27 inches of rain on average.

Additionally, the Sonoma County Water Agency, which provides 75-80% of the district’s annual supply through Russian River water imports, had cut imports by 20% that summer as it faced shortages at its own two reservoirs, Lake Mendocino and Lake Sonoma. The utility has since reinstituted the 20% import reduction this summer in response to low water supplies.

Stafford Lake is the district’s only backup supply and is usually drawn on during the summer, when water consumption can double. The lake can hold about 4,300 acre-feet of water and makes up about 25% of Novato’s water supply.

The district also has the ability to pump Russian River water into the reservoir during the more flush winter months to hold in reserve until it is needed. Anticipating a dry 2020-2021 winter, the district spent $400,000 to resupply the reservoir that winter. The bet paid off — the lake would have otherwise gone dry later that year.

Tony Williams, the general manager of the North Marin Water District, said that while the primary focus is working to bolster supplies from Sonoma County, the supply at Stafford Lake acts as a buffer in case more severe cuts are implemented.

“The local supply comes into play, especially in these situations where we have to cut back,” Williams said. “To provide some resiliency and redundancy, our Stafford supply helps us get through those times. That is the primary focus. It’s not 100% resiliency. We can’t duplicate what we get from Sonoma Water, but it’s providing a little bit of a buffer.”

The study is recommending the district expand its local supply by as much as 2,000 acre-feet to keep up with water demand from projected population growth in the Novato area. Water demand is set to increase by 2,300 acre-feet in Novato, or about 26%, within the next 25 years, according to the study.

The district is looking at options to install an adjustable sluice gate on the Stafford Lake spillway that would allow the reservoir to hold an additional 726 acre-feet of water — about a 17% increase. Additionally, the district is set to launch a pilot test at its Stafford treatment plant to test whether there are ways to yield more potable water and reduce waste when it treats Stafford Lake supplies. The study estimates this could yield an additional 20 to 70 acre-feet of water per year.

Williams said the district has already earmarked $50,000 to conduct a deep dive into all of the regulatory approvals and environmental impact analyses that might be needed for the sluice gate project.

While the project would not involve dredging sediment from the lake bottom or raising the dam, Williams said it will likely require changes to its water rights, which would require a potentially lengthy review by the state water board.

“That actually sounds like a really simple project but it’s really complicated from a permitting and engineering standpoint,” Williams said.

The sluice gate would cost about $90 per acre-foot of additional storage, according to the study. By comparison, dredging Stafford Lake to add about 550 acre-feet of storage is estimated to cost $2,600 per acre-foot. The treatment plant upgrades would cost $70 to $240 per acre-foot, according to the study.

District board member Mike Joly said he supports these projects to provide at least some short-term relief as the district looks at more regional water supply projects.

“I think for bang for the buck and for immediacy, yes,” Joly said in regard to his support. “We need to be seen to be enhancing our water supply for our customers. That’s important.”

The sluice gate is estimated to cost about $1.5 million, which Williams said could be covered by part of a $20 million loan the district received for facilities upgrades, including its $11 million upgrade to its administrative building and laboratory.

The study also identified other longer-term options that might require support from other water suppliers, including the Marin Municipal Water District and the Sonoma County Water Agency.

These options included capturing stormwater runoff from Bowman and Leveroni canyons. The study evaluated various options, ranging from pumping the water back into Stafford Lake to building a new dam across the canyons.

Pumping the water to Stafford would yield an estimated 93 to 788 acre-feet of water per year at costs ranging from $330 to $960 per acre-foot, depending on the option, according to the study. Damming the canyons would provide an estimated 175 acre-feet and 753 acre-feet of water per year, respectively, at a cost of $1,700 and $800 per acre-foot, respectively.

Other options, such as a local desalination plant, were deemed infeasible because of the high costs and regulatory approvals that would be required of such as small water district, according to the study. However, Joly said there might be opportunities to partner with other Bay Area water agencies to construct a regional desalination plant.

“There is just an incredible irony that we could have a water problem, being next to the largest body of water on the planet,” Joly said. “It’s just something that just catches your eye immediately. But there is a lot of work to do for desalination.”

The Marin Municipal Water District is also evaluating regional projects such as desalination as part of its own ongoing study into new water supplies.

“We’re collaborating with Marin Water as much as we can and we’re interested in partnering on a future project if that makes sense for something like desal,” Williams said. “We wouldn’t do it by ourselves.”

More information about the water supply study can be found at nmwd.com/save-water/new-water-supplies/.

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